Since man first began to heat and cool the enclosures within which he lives and works, there has been a problem in maintaining an even temperature.
When the enclosures or structures have been heated by means such as the burning of combustibles, whether in a fireplace, stove, or furnace, high heat is achieved during the burn with a dropping of temperature between firings.
Although the use of solar energy to at least supplement the heating of structures has been known and experimented for many years, it has only been since the fossil fuel shortages of the mid-1970's that this source of heat has been seriously considered.
In all solar systems, whether active or passive, the problem of storing the heat obtained during favorable times and conditions for later release and use during unfavorable times and/or conditions has been of primary concern.
Floor and wall tiles, bricks, cement blocks and the like have been used as heat storage means. Since these have almost universally proved to be inadequate, additional storage means such as liquid filled jugs and drums and similar means have been used to supplement and add to the storage capacity. The problem with these various means has been that, first they generally do not store the amount of heat necessary and secondly, they take up tremendous amounts of space which otherwise could be used as living or working areas.